1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) element, and more particularly to such the organic EL element improved in its sealing structure.
The present application claims priority of Japanese Patent Application No. Hei 11-357653 filed on Dec. 16, 1999, which is hereby incorporated by reference.
2. Description of the Related Art
In a conventional organic EL element, in order to improve the organic EL element in brightness, the organic EL element has its negatibe electrode (cathode) made of a material such as alkali metals or a like which are excellent in electron injection properties. Further, as a material of its organic EL compound (medium) layer, the organic EL element employs a material excellent in light-emitting efficiency. However, such conventional organic EL element is still disadvantageous in that a so-called xe2x80x9cdark spotxe2x80x9d often appears in its display panel. This dark spot is constructed of an electroluminescence-disabled region resulting from deterioration in material properties of an organic EL medium and/or from exfoliation of the negative electrode. Such deterioration in material properties and such exfoliation of the negative electrode are caused by presence of oxygen or moisture in an atmosphere around the organic EL element to make the organic EL element poor in its light-emitting properties such as brightness, chromaticity and a like. Consequently, in order to improve the organic EL element in this respect, heretofore, various countermeasures have been taken against the dark spot.
For example, Japanese Patent Application Laid-open No. Hei 9-148066 discloses a method for decreasing humidity of the atmosphere around the organic EL element by using a dehydrating agent (drying agent) disposed in a sealed space provided inside the organic EL element. More specifically, in such the sealed space of the organic EL element, the dehydrating agent is oppositely disposed from the negative electrode so that the humidity of the atmosphere in the sealed space of the organic EL element is effectively decreased.
FIG. 5 is a cross-sectional view of the conventional organic EL element fabricated according to this prior art. As shown in FIG. 5, the conventional organic EL element has a construction in which: a transparent electrode (positive electrode, anode) 2 is made of a light-transmissive Indium-Tin Oxide (ITO), and formed on a glass substrate 1; and, subsequently formed on this transparent anode electrode 2 are an organic EL layer 3 and a negative electrode 4, wherein the organic EL layer 3 is constructed of a hole injection/transport layer, a light-emitting layer, an electron injection/transport layer or a like. In order to prevent the organic EL element from deteriorating in light-emitting properties, as shown in FIG. 5, a dehydrating agent 6 is fixedly mounted on an inner surface of a sealing member 7 in a space 8 defined by the sealing member 7, and serves as a drying agent therein.
On the other hand, Japanese Patent Application Laid-open No. Hei 7-169567 discloses a technique for preventing moisture from entering the organic EL element by using a protective layer. More specifically, such protective layer contains a dehydrating agent or any other materials suitable for absorbing or consuming oxygen and moisture, and is laminated to an outer surface of an assembly of a positive electrode, an organic EL layer and a negative electrode in the organic EL element.
Further, Japanese Patent Application Laid-open No. Hei 10-275682 discloses a method for preventing moisture from permeating a surface of the organic EL element by blocking out the moisture from the atmosphere. More specifically, in this conventional organic EL element: a protective layer, which is made of a fluorine-based high polymeric substance or of an oxide insulation material, is formed on a negative electrode of the organic EL element; and, further, a sealed space of this organic EL element is filled with an inert medium containing a dehydrating agent.
Now, the problems to be solved by the present invention will be described.
In the above-mentioned Japanese Patent Application Laid-open No. Hei 9-148066 in which the dehydrating agent 6 is oppositely disposed from the negative electrode 4, since an adhesive is used to fixedly mount the sealing member 7, considerable care should be taken not to damage the dehydrating agent, which complicates a fabrication process of the conventional organic EL element. Further, even this conventional organic EL element is still not free from the organic EL element deterioration problem caused by moisture, wherein the moisture enters the space 8 of the organic EL element through a contact area between the glass substrate 1 and the sealing member 7 bonded to this glass substrate 1, and adheres to a surface of the negative electrode 4 to deteriorate the organic EL element.
On the other hand, in the Japanese Patent Application Laid-open No. Hei 7-169567 in which the protective layer containing the dehydrating agent or any other material suitable for absorbing or consuming oxygen and moisture is laminated to the outer surface of the assembly of the positive electrode, the organic light-emitting material and the negative electrode, the protective layer is provided over a surface of the negative electrode. However, the dehydrating agent contained in the protective layer tends to absorb the moisture to gradually permit a leakage electric current to increase, which deteriorates the light-emitting properties of the conventional organic EL element.
Lastly, with respect to the Japanese Patent Application Laid-open No. Hei 10-275682 having a construction in which: the protective layer, which is made of a fluorine-based high polymeric substance or of the oxide insulation material, is formed on the negative electrode; and, the sealed space of this conventional organic EL element is filled with the inert medium containing the dehydrating agent in order to block the moisture from the atmosphere, it is hard to prepare the inert medium itself, and also hard to filling it in the sealed space of the organic EL element. In addition to the above disadvantages, this prior art is disadvantageous in that it is difficult to have the negative electrode brought into intimate contact with the protective layer, which permits the moisture of the atmosphere to enter the sealed space of the organic EL element through a boundary between the negative electrode and the protective layer.
In view of the above, it is an object of the present invention to provide an organic electroluminescent (EL) element, which is excellent in sealing properties thereof, and therefore capable of solving the above problems inherent in the prior arts.
According to a first aspect of the present invention, there is provided an organic electroluminescent element having its components arranged in a multi-layer stack in which the components include a positive electrode, an organic electro-luminescent layer and a negative electrode, and are subsequently deposited on a substrate, in which the organic electro-luminescent layer includes a hole injecting/transporting layer, a light-emitting layer, an electron transporting layer, wherein:
a protection film is formed on the negative electrode; a dehydrating agent is provided over the protection film; and all the components of the organic electroluminescent element are sealed by combining a sealing member with the substrate.
In the foregoing, a preferable mode is one wherein the dehydrating agent is made of a chemical compound capable of keeping its solid state even when taking up moisture, or made of a chemical compound capable of gelling when taking up moisture, and is formed into a powder or a film.
Also, a preferable mode is one wherein the dehydrating agent is coated with a porous sheet; and, an adhesive provided in an end portion of the porous sheet is used to bond the porous sheet to a surface of the protection film, whereby the dehydrating agent is fixedly mounted on the surface of the protection film.
Also, a preferable mode is one wherein the dehydrating agent is contained in a porous casing; an adhesive provided in an end portion of the porous casing is used to fixedly bond the dehydrating agent to a surface of the protection film.
Further, a preferable mode is one wherein a space defined and sealed by both the substrate and the sealing member is filled with an inert gas.
Also, according to a second aspect of the present invention, there is provided an organic electroluminescent element having its components arranged in a multi-layer stack in which the components include a positive electrode, an organic electroluminescent layer and a negative electrode, and are subsequently deposited on a substrate, in which the organic electroluminescent layer includes a hole injecting/transporting layer, a light-emitting layer, an electron transporting layer, wherein:
a composite protection film including a lower layer and an upper layer is formed in a manner such that the lower layer is disposed on the negative electrode and the upper layer is disposed on the lower layer; a dehydrating agent is provided over the composite protection film; and all the components of the organic electroluminescent element are sealed by combining a sealing member with the substrate.
In the foregoing second aspect, a preferable mode is one wherein the lower layer of the composite protection film is made of same chemical compound or its derivative used in the electron transporting layer.
A preferable mode is one wherein the upper layer of the composite protection film is made of a fluorine-based lubricant or of a diamond-like carbon.
Also, a preferable mode is one wherein a barrier metallic film is provided between the upper layer and the lower layer of the composite protection film.
Also, a preferable mode is one wherein a side surface of each of the negative electrode and the organic electroluminescent layer is coated with same material used in said upper layer of said composite protection film.
Also, a preferable mode is one wherein a side surface of each of the negative electrode, the barrier metallic film and the organic electroluminescent layer is coated with same material used in said upper layer of said composite protection film.
Also, a preferable mode is one wherein the dehydrating agent is made of a chemical compound capable of keeping its solid state even when taking up moisture, or made of a chemical compound capable of gelling when taking up moisture, and is formed into a powder or a film.
Also, a preferable mode is one wherein the dehydrating agent is coated with a porous sheet; and, an adhesive provided in an end portion of the porous sheet is used to bond the porous sheet to a surface of the upper layer of the composite protection film, whereby the dehydrating agent is fixedly mounted on the surface of the upper layer of the composite protection film.
Also, a preferable mode is one wherein the dehydrating agent is contained in a porous casing; an adhesive provided in an end portion of the porous casing is used to fixedly bond said dehydrating agent to a surface of the upper layer of the composite protection film.
Further, a preferable mode is one wherein the barrier metallic film is constructed of an aluminum film or of aluminum alloy film.
Still further, a preferable mode is one wherein a space defined and sealed by both the substrate and the sealing member is filled with an inert gas.
With the above configurations, it is possible to coat the negative electrode with the protection film, which makes it possible to directly fix the dehydrating agent to the protection film by using the porous sheet. This makes it possible to seal up the organic EL element of the present invention in an easy manner.
Also, the protection film is constructed of the composite film which includes: the lower layer made of the same material used in the electron transporting layer of the organic EL layer; and, the upper layer made of the fluorine-based lubricant and the like. Consequently, it is possible to have the negative electrode brought into more intimate contact with the protection film, which improves the sealed structure of the organic EL element of the present invention in humidity resistance and therefore in reliability.
Further, it is possible for additional provision of the barrier metallic film between the upper layer and the lower layer to further improve the sealed structure of the organic EL element of the present invention in humidity resistance.